Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)
CWE-391 Base Incomplet
Unchecked Error Condition
This vulnerability occurs when a program fails to properly check or handle error conditions, such as exceptions or return codes. By ignoring these failures, the software can enter an unexpected…
Définition
What is CWE-391?
This vulnerability occurs when a program fails to properly check or handle error conditions, such as exceptions or return codes. By ignoring these failures, the software can enter an unexpected state that attackers might exploit, often without any logging or user notification.
When your code doesn't check for errors—like a failed file operation, a null pointer, or a network timeout—it continues executing as if nothing went wrong. This creates a gap between what the program assumes is true (e.g., 'the data was loaded') and reality (e.g., 'the variable is empty'), leading to crashes, data corruption, or security bypasses. Attackers can deliberately trigger these ignored errors to destabilize your application or reveal sensitive information.
To prevent this, always implement robust error handling. Check return values from functions, use try-catch blocks for exceptions, and validate system call outcomes. Log all caught errors with sufficient context for debugging, and decide on safe failure modes—like rolling back transactions or terminating the session—instead of silently proceeding. This defensive practice closes a common attack vector and makes your software more resilient and observable in production.
Impact réel
Real-world CVEs caused by CWE-391
Aucune référence CVE publique n'est liée à ce CWE dans le catalogue MITRE pour le moment.
Comment les attaquants l'exploitent
Parcours de l'attaquant étape par étape
- 1
Identifier un chemin de code qui traite des entrées non fiables sans validation.
- 2
Élaborer une charge utile qui exploite le comportement non sécurisé — injection, traversal, débordement ou abus de logique.
- 3
Délivrer la charge utile via une requête normale et observer la réaction de l'application.
- 4
Itérer jusqu'à ce que la réponse divulgue des données, exécute le code de l'attaquant ou élève les privilèges.
Exemple de code vulnérable
Vulnerable Java
The following code excerpt ignores a rarely-thrown exception from doExchange().
try {
doExchange();
}
catch (RareException e) {
```
// this can never happen*
} Exemple de code sécurisé
Secure pseudo
// Validate, sanitize, or use a safe API before reaching the sink.
function handleRequest(input) {
const safe = validateAndEscape(input);
return executeWithGuards(safe);
} What changed: the unsafe sink is replaced (or the input is validated/escaped) so the same payload no longer triggers the weakness.
Liste de contrôle de prévention
How to prevent CWE-391
- Requirements The choice between a language which has named or unnamed exceptions needs to be done. While unnamed exceptions exacerbate the chance of not properly dealing with an exception, named exceptions suffer from the up call version of the weak base class problem.
- Requirements A language can be used which requires, at compile time, to catch all serious exceptions. However, one must make sure to use the most current version of the API as new exceptions could be added.
- Implementation Catch all relevant exceptions. This is the recommended solution. Ensure that all exceptions are handled in such a way that you can be sure of the state of your system at any given moment.
Signaux de détection
How to detect CWE-391
Plexicus détecte automatiquement CWE-391 et ouvre une PR de correction en moins de 60 secondes.
Codex Remedium analyse chaque commit, identifie cette faiblesse précise et livre une pull request prête à être relue avec le correctif. Pas de tickets. Pas de transferts.
Questions fréquentes Qu'est-ce que CWE-391 ?
Quelle est la gravité de CWE-391 ?
Quels langages ou plateformes sont affectés par CWE-391 ?
Comment puis-je prévenir CWE-391 ?
Comment Plexicus détecte et corrige CWE-391 ?
Où puis-je en savoir plus sur CWE-391 ?
Frequently asked questions
Qu'est-ce que CWE-391 ?
This vulnerability occurs when a program fails to properly check or handle error conditions, such as exceptions or return codes. By ignoring these failures, the software can enter an unexpected state that attackers might exploit, often without any logging or user notification.
Quelle est la gravité de CWE-391 ?
MITRE évalue la probabilité d'exploitation comme Moyenne — l'exploitation est réaliste mais nécessite généralement des conditions spécifiques.
Quels langages ou plateformes sont affectés par CWE-391 ?
MITRE n'a pas spécifié les plateformes affectées pour ce CWE — il peut s'appliquer à la plupart des stacks applicatives.
Comment puis-je prévenir CWE-391 ?
The choice between a language which has named or unnamed exceptions needs to be done. While unnamed exceptions exacerbate the chance of not properly dealing with an exception, named exceptions suffer from the up call version of the weak base class problem. A language can be used which requires, at compile time, to catch all serious exceptions. However, one must make sure to use the most current version of the API as new exceptions could be added.
Comment Plexicus détecte et corrige CWE-391 ?
Le moteur SAST de Plexicus reconnaît la signature de flux de données de CWE-391 à chaque commit. Lorsqu'une correspondance est trouvée, notre agent Codex Remedium ouvre une PR de correction avec le code corrigé, les tests et un résumé d'une ligne pour le relecteur.
Où puis-je en savoir plus sur CWE-391 ?
MITRE publie la définition canonique à https://cwe.mitre.org/data/definitions/391.html. Vous pouvez également consulter la documentation OWASP et NIST pour des conseils adjacents.
Faiblesses associées
Weaknesses related to CWE-391
CWE-754 Parent
Improper Check for Unusual or Exceptional Conditions
This weakness occurs when software fails to properly anticipate and handle rare or unexpected runtime situations that fall outside normal…
CWE-252 Frère
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CWE-253 Frère
Incorrect Check of Function Return Value
This vulnerability occurs when a program misinterprets or improperly validates the return value from a function, causing it to miss…
CWE-273 Frère
Improper Check for Dropped Privileges
This vulnerability occurs when an application tries to lower its system privileges but fails to verify that the operation was successful.
CWE-354 Frère
Improper Validation of Integrity Check Value
This vulnerability occurs when software fails to properly check the integrity of data by validating its checksum or hash value. Without…
CWE-394 Frère
Unexpected Status Code or Return Value
This vulnerability occurs when software fails to properly validate the full range of possible return values from a function or system…
CWE-476 Frère
NULL Pointer Dereference
This vulnerability occurs when a program attempts to access or manipulate memory using a pointer that is set to NULL, causing a crash or…
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